Apparatus and method for sealing a lid onto a container

ABSTRACT

A modular type replaceable heating unit with a downwardly facing heating ring for use in an apparatus for sealing a flat lid with a lower layer of heat bondable material onto the upper, generally flat surface of a flange extending around the periphery of an access opening in a container. The apparatus moves the heating unit between first and second positions. The apparatus includes a generally fixed high frequency power supply for energizing the heating ring, connecting the high frequency power supply to the heating ring only while the heating unit is moving between the first and second positions. The ring is forced against the lid as the power supply is energized and is released from the lid after the power supply has been de-energized. Preferably the ring is an inductor. A plurality of these heating units is carried by a turret to define individual heating stations on the turret which stations rotate to selectively energize the individual heating units. The heating units include means for coupling with the moving means of the apparatus and a transformer for energizing the heating ring.

This is a continuation of application Ser. No. 07/476,555, filed Feb. 7,1990, now abandoned which is a divisional application of applicationSer. No. 07/254,837, filed Oct. 7, 1988, now U.S. Pat. No. 4,941,306.

DISCLOSURE

The present invention relates to the art of packaging a mass producedsubstances, such as food products, so they will have a long shelf life,and more particularly to an improved apparatus and method for heatsealing a lid onto a container filled with such products.

INCORPORATION BY REFERENCE

Mohr's U.S. Pat. No. 4,707,213 discloses an apparatus for sealing agenerally flat lid with a lower layer of heat bondable material onto aflange surface extending around the periphery of an access opening to acontainer for hermetically storing a substance susceptible todeterioration when exposed to atmosphere for a prolonged time, such as aprepared food product, by using a non-water cooled inductor for pressingthe lid against the flange and then inductively heating a metal layer onthe laminate from which the lid is stamped to raise the temperature ofthe lower heat bondable material of the lid liminate to the sealingtemperature as pressure is maintained, so that the lid is sealed ontothe container by setting of the heat bondable material. This patentdiscloses background information to which the present invention isdirected and is incorporated herein for the purpose of illustrating thisgeneral background information and environment of the present invention.

BACKGROUND OF THE INVENTION

Most prepared food products, after they are prepared and ready for massdistribution through retail outlets, must be packaged, distributed andsold in a manner to prevent deterioration over prolonged periods oftime, referred to as "shelf life". Over the years the food industry hasdeveloped many packaging and distributing processes for accomplishingthe objective of instilling food substances with a long shelf life.Cans, jars, frozen or refrigerated containers, and hermetically sealedplastic packages or containers are the more common processes andpackaging for this purpose. These procedures have presented certaindisadvantages generally associated with either the expense of thepackaging or the cost of refrigerating, freezing and maintaining thepressuring condition of the food packages as they progress through theretail channels. In view of this situation, there has been a tremendouseffort in the food industry to develop inexpensive, serving sizecontainers for prepared foods which need not be frozen and/orrefrigerated to accomplish an acceptable shelf life. One of the moresuccessful approaches in the quest by the food industry to accomplishthis objective has been the development of a plastic container having anappropriate gas barrier layer to prevent oxygen migration through thewalls of the container and incorporating an upper lid formed from alaminate and also having an oxygen migration barrier which is heatbonded by an appropriate bonding material layer over the access openingof the plastic container. By merely placing the prepared food into thecontainer and heat bonding the lid thereto, oxygen cannot enter thecontainer through the container itself or through the upper lid. Byremoving oxygen from the container before the lid is sealed onto thecontainer either by drawing a vacuum, purging the container with asniner gas and/or both of these procedures, oxygen is excluded fromassociation with the packaged food product to accomplish a long,acceptable shelf life. This new packaging concept is now becoming quitecommon and is used for many products. In accordance with one knownprocedure, the laminated lid is sealed onto the container by employing aheated ring forced against the lid so that the heat energy of the ringis conducted to the layer of heat bondable material between the lid andcontainer flange whereby the heat bondable layer is heated and seals thelid onto the container in a path of "footprint" defined by the shape ofthe ring. Although this procedure does operate and is being widelyemployed in the food industry, there are distinct disadvantages. Heatingof the ring for conducting heat energy from the ring to the heatbondable material cannot be accomplished rapidly. In addition, the ringdoes not cool rapidly. It is critical to keep the ring in place untilthe seal is set. Consequently, the heating cycle for heating andallowing the ring to cool is relatively long. Further, uniform heatingaround the surface of the ring and adjustment of the heating effect toaccomplish optimum sealing is difficult, if not impossible, toaccomplish.

In view of the substantial disadvantages associated with a heated ringto heat the bonding material by conduction for sealing the lid onto thecontainer, a relatively new technique has developed wherein the ring isan inductor and a metal layer is incorporated into the laminated sheetmaterial forming the lid, so that as a high frequency is applied to theinductor, the metal layer in the lid material itself is heated only inthe area adjacent the inductor. By forcing the inductor against the lid,induction heating of the metal in the lid directly below the inductorcauses sealing of the heat bondable material sandwiched between the lidand the container. Immediately upon de-energizing the inductor, heat isremoved from the metal layer of lid and final sealing is accomplished.In this manner, accurate control may be maintained over the heat sealingfunction so that the lid can be economically and rapidly applied ontothe container to accomplish sealing of the container in a fashion whichcan be repeated from one container to the next. Mohr's U.S. Pat. No.4,707,213 illustrates induction heating of a metal layer for the purposeof sealing a lid onto the container which has proven successful,reliable and repeatable.

THE INVENTION

The present invention relates to improvements over prior inductionheating apparatus and methods for heat sealing the metallized lid over aplastic container to provide a hermetically sealed, mass producedcontainer for substances which are susceptible to deterioration whenexposed to atmosphere for a prolonged time, such as prepared foodproducts. These improvements have been developed for converting ainduction heating heat seal apparatus and method into an efficient, highspeed machine to control the operating parameters of the inductionheating process while maintaining the overall cost of the machinerelatively low. Thus, the present invention is directed towardimprovements in an induction heating type sealing apparatus and method,which improvements produce uniform results, at high speed, without theneed for extremely expensive equipment.

The invention will be described with particular reference toimprovements in an induction heating type of sealing apparatus; however,certain aspects of the invention have broader applications and areapplicable even to conduction type heating apparatus over which theinduction heating process is a substantial advance.

By using the present invention, high frequency components can beemployed for the induction heating process. High frequency generallyrelates to radio frequency and primarily frequency exceeding 25 KHz. Thepreferred embodiment employs at least about 50 KHz; consequently thecomponents can be relatively small to reduce the weight of he componentsand, thus, the mass for the purpose of reducing acceleration forces andmomentum so that the equipment can be operated at the necessary highspeeds to make the invention acceptable for high speed sealing ofcontainers. Consequently, the thermal sealing technique is performed byhigh frequency power to reduce the mass and associated inertia for highspeed operation. Since high frequency components can be used inpracticing the present invention so that the inductor itself and theassociated electrical transmission structures for directing electricalenergy to the heating process itself need not include liquid cooling.Consequently, the normal procedure for induction heating apparatuswherein liquid cooling is required is overcome by application of uniqueconcepts that allow high frequency operation of the apparatus. Byemploying the present invention, not only can the heating process beperformed at high speeds; but, dry switching and high energydistribution from a single power supply is obtained by a multiplexingarrangement which does not hinder the accurate control over heating ofeach container. Each container is processed in a fashion which essentialguarantees that a seal is formed at the desired consistency in afootprint extending completely around the access opening of thecontainer. In this fashion, and by using the present invention, highspeed sealing is accomplished without sacrifice of the uniformity of theheat seal, together with a consistency of the heat seal that balancesthe diverse need for an air tight seal and a lid that can be peeled fromthe container uniformly, without requiring complex manual manipulativeefforts.

The present invention also allows the application of discrete energybursts that can be controlled for each individual sealing operationperformed by the apparatus from one container to the next. As will beexplained later, the invention employs a large number of discreteheating and sealing stations that are energized in series as thestations move along a preselected path in a fashion to allow sufficienttime for each individual sealing operation to be performed at oneposition, while the lid is placed on the station at another position andas filled container is loaded onto the apparatus at another position. Byemploying the present invention, all of these functions necessary toseal a container can be accomplished in series to accomplish high speedoperation while also providing sufficient time to evacuate air from thecontainer and flush the container with gas. All of these functionsrequire substantial time; but, they can be accommodated by using theinvention without diminishing the overall production rate at whichcontainers are sealed. The invention allows total automation of thesealing procedure so that the high speed production rates areaccomplished on a large number of containers at a high speed withoutmanual intervention.

By employing the unique technique of energy monitoring and control, eachindividual heating operation for a given container can be optimized toreduce the necessity for substantial and expensive post sealing qualitycontrol procedures. Consequently, by employing the present invention,the actual sealing procedure can be so meticulously controlled that thenormal inspection and quality accuracy associated with food products maybe decreased without sacrificing the overall confidence in the qualityof the product being packaged. Thus, quality can be controlled by usingthe invention properly to reduce need for normal quality control checks,such as 100% pressure testing.

The present invention, as explained previously, relates to a concept ofemploying a high frequency power supply. In accordance with an aspect ofthe invention, this power supply has an output voltage which iscompatible with a relatively long, high frequency transmission line andutilizes an impedance matching arrangement that compliments thelightweight, non-water cooled components associated with the presentinvention, so that the induction tooling equipment performing the actualsealing function can be placed and aranged on an apparatus to produce anoptimum high speed operation. By incorporating the present invention,the heating function itself dictates the position, movement andoperation of the actual mechanical devices causing the sealing. In thepast, the heating equipment and manipulation devices associated with thesealing function dictated not only the speed at which the apparatuscould be operated but also in what fashion these components would bearranged, assembled and operated. By employing high frequency and thisaspect of the invention, the mechanical apparatus can be arranged andoperated to optimize the sealing function, the ultimate purpose of thistype of apparatus and method.

In accordance with another aspect of the present invention, a unique dryswitching system is provided for distributing the high frequency powerthrough electrical connections that employ a common, fixed power supplythrough a communicating type, switching plate for individually applyingpower, in sequence, to a number of individual heating and sealingstations as they all move on the apparatus. The dry switching of thehigh frequency power supply from one station to the other, in sequence,is accomplished by structural elements which are integral feaures of thelightweight rotary sealing apparatus. Consequently, the apparatus andits single power supply can provide a uniform individually controllableenergy burst to each of the sealing stations at the sealing position asthe stations move in succession through a fixed path hrough he heaingposition. In accordance with a preferred embodiment of the invention, aprogrammable controller is employed for establishing the heating andsealing cycle of an apparatus constructed in accordance with the presentinvention so that the single high frequency power supply can bemultiplexed at the proper time through a novel dry switching arrangementto apply high frequency current through an inductor or heating ring toseal the lid onto the container. In a fashion current can be turned onand then turned off during a heating cycle tailored to seal a singlecontainer on a particular moving station.

By the concept of integrating the instantaneous power at the powersupply, as a function of time, to create an energy signal representingthe energy actually applied to a heating station during a specificmonitored heating cycle can be used to accurately monitor he energyburst at each station. The summation of the energy output or burstduring a heating cycle for a given container can be compared to apreselected desired reference energy level or burst for the purpose ofcontrolling the amount of energy actually supplied to the inductionheating inductor during each sealing cycle. Thus, an energy burstcomplying with the particular need of the container being processed isobtained. By employing the invention, the energy supplied to eachindividual container process, in sequence, can be controlledindividually.

The present invention also relates to the concept of utilizing a heatingunit carrying the heating ring using a unique and novel moduleconstruction that can be plugged into the system or apparatus at eachmoving heating station for the purpose of rapidly replacing a heatingunit. This avoids lengthy down time and substantial replacement costs.Further replacement units can be available for use so the machine isinoperative for only a short time to change heating units.

The primary object of the present invention is the accomplishments ofthe improvements of the present invention, as set forth above, whichimprovements are obtained, in accordance with the present invention, byproviding an improvement in a device for sealing a flat lid with a lowerlayer of heat bondable material onto the upper surface of a generallyflat flange extending around the periphery of the access opening in acontainer for hermetically storing a substance susceptible todeterioration when exposed to atmosphere for a prolonged time. Thisdevice, which is improved by the invention, includes means for placingthe lid over the flange with the layer of heat sealable plastic materialsandwiched between the lid and the flange to define a closed loopsealing area with a shape defined by the lid and flange, a heating unitincluding a body, a heat energy transfer ring carried by the body with ashape generally matching the closed loop shape of the sealing areabetween the lid and container, means for forcing the heating unitagainst the lid to clamp the lid against the flange, means for causingthe ring to heat the bondable plastic material in a closed loop patternor footprint defined by the shape of the ring and means for removing theheating unit from the lid after the lid is bondedor set, at leastpartially. The invention is the improvement which involves providingmeans for moving the heating unit in a preselected path between firstand second positions, a high frequency power supply in a fixed positionrelative to the moving heating units and means for energizing the ringwith the fixed power supply as the heating unit is moving between thefirst and second positions to define a heating cycle. By employing thepresent invention, the high frequency power supply is fixed and theindividual heating units can be movable with a slip ring or switch platearrangement between the fixed power supply and the movable heating unitscarried on heating stations so that a plurality of heating units can beenergized in succession by appropriate, successive operation of a singlehigh frequency power supply which can be rapidly energized andde-energized.

In accordance with still another aspect of the present invention, thereis provided a device for sealing a flat lid with a lower layer of heatbondable material, of the type defined above, onto a plastic container,which device includes a turret having a given number ofcircumferentially spaced stations, means for rotating said turret abouta vertical axis whereby the stations move along a generally circularpath, means for loading a container filled with the substance, such as aprepared food product, onto a station of the turret at a first positionon the path, means for locating a lid over the filled container at asecond position on the path, and means for heating the heat bondablematerial while the lid is forced against the flange of the container ata third position on the path whereby the lid is heat sealed onto theflange of the container. This heating means includes a heating unitlocated at each of the moving stations including a downwardly facingheating ring adapted to force the lid against the flange and electricalmeans for causing the ring to heat the lid in a pattern or footprintdefined by the ring and extending around the flange periphery, wherebythe heat bondable material is heated to a lid sealing temperature alongthe pattern at this third position. The electrical means for causingheating by the ring comprises a high frequency power supply fixedlymounted with respect to the rotatable turret, a dry switch plate havinga number of circumferentially spaced contacts rotatable with the switchplate as it is rotated in unison about the axis, bus means on the turretfor fixedly connecting each ring of each of the heating units at a givenposition to a selected contact of the switch plate, and brush meansconnected to the high frequency power supply and including brushcontacts riding on the switch plate. The contacts on the switch plateare spaced to correspond with the given number of moving stations sothat the heating units are energized, in succession, by the power supplyto define a heating cycle occurring when the heating unit is at thethird position of the path through which the heating unit is moved bythe turret.

In accordance with still another aspect of the invention, the lid of thecontainer is sealed onto the top of the container by a method employingthe apparatus as defined above. In this manner, the basic objective isaccomplished where a high speed machine and method of operating themachine allows accurate control of the individual heating cycles byemploying high frequency, low mass components in a unique configurationproducing a unique and novel overall system apparatus and method.

BRIEF DESCRIPTION OF DRAWINGS

In this disclosure, the preferred embodiment of the invention isillustrated in the following drawings:

FIG. 1 is a side elevational view, somewhat in cross section,illustrating the preferred embodiment of the present invention;

FIG. 2 is a top plan view taken generally along line 2--2 of FIG. 1;

FIG. 3 is a partial cross sectional view taken generally along line 3--3of FIG. 2;

FIG. 4 is an enlarged, partially cross sectioned, partial sideelevational view of the preferred embodiment of the present inventionillustrating a single station;

FIG. 5 is a cross sectional view of the heating unit module employed inthe preferred embodiment of the present invention;

FIG. 6 is a cross sectional view taken generally along line 6--6 of FIG.5;

FIG. 7 is a partial, pictorial view showing the inductor and matchingtransformer employed in the heating unit module of FIGS. 5 and 6;

FIG. 8 is a block diagram illustrating a power monitor concep to be usedin the present invention;

FIG. 9 is a logic diagram, and partial block diagram and wiring diagram,of the control flow chart employed in accordance with the preferredembodiment of the present invention;

FIG. 9A is a diagram of a modification of the preferred embodiment shownin FIG. 9;

FIG. 10 is a graph illustrating the power multiplexing of a single powersupply to the individual heating units of the preferred embodiment ofthe present invention;

FIG. 11 is a power curve showing in detail certain timing functions andthe shape of the energy burst employed in accordance with certainaspects of the present invention; and,

FIG. 12 is a modified power curve showing a different energy burst shapeusable in practicing the present invention.

PREFERRED EMBODIMENT

Referring now to the drawings wherein the showings are for the purposeof illustrating a preferred embodiment of the invention only, and notfor the purpose of limiting same, FIGS. 1 and 2 show an apparatus A forthe purpose of bonding a lid L formed from laminated sheet material ontoa container C containing a substance which can deteriorate by long termexposure to oxygen, such as a prepared food products. The food productis deposited into the container which is then loaded onto a turret T atloading position I shown in FIG. 2. Turret T is rotated to a position IIwhere the lid or cover L is deposited over the filled container C.Thereafter, the lid is heated selectively around its periphery for thepurpose of sealing the lid onto the top of the container to preservefood product F encapsulated within the container. As a primary supportelement turret T includes a rotating table 10 supported on bearing 12 insupport race 14, as best shown in FIG. 1. Rotatable table 10 has aplurality of circumferentially spaced heating stations, identified asstations S1-S16, equally spaced in a circumferential direction aroundthe outer periphery of table 10 to rotate about axis a. In the preferredembodiment of the invention, sixteen heating stations are provided onturret T; however, any number of circumferentially spaced heatingstations could be used to practice the invention. Integrally formed withtable 10 is a lower stabilizing plate or base plate 20 having aplurality of radially extending slots 22 for each heating station. Eachheating station includes, as a separate element, a lower containersupporting nest 30 adapted to receive the container C after it has beenfilled with the food product F. In the preferred embodiment, nest 30 ateach station S1-S16 has downwardly extending, spaced posts 40, 42adapted to ride within a slot 22 at each station so that the nest ateach station can be moved radially inwardly or radially outwardly as thestations move in he direction of the arrow shown in FIG. 2. A variety ofstructures could be employed for reciprocating nest 30 in a radialdirection on plate 20 as table 10 is rotaed; however, in the preferredembodiment, post 42 is elongated and extends into a cam groove 44 whichacts upon post 42 to move nest 30 in slot 22 as turret T rotates aboutaxis a. As so far described, a filled container C is loaded onto itsnest 30 at position I. The nest is then moved inwardly and lid L isplaced over the container in the nest. Thereafter, nest 30 movesinwardly and is carried by turret T toward the heating location orposition III. During this rotary movement, a vacuum is applied under thelid and inside the container to remove oxygen from the container. Atheating station III, the lid L is inductively heated, in a manner to beexplained later, for sealing the lid onto the container at flange or rimR. Until the lower layer of heat bondable material M is set, the lid isheld against the container. When the seal has stabilized, the nest 30 ismoved outward along groove 22 at a circumferential position shown asbeing between station S9 and station S16 in FIG. 2. Thereafter, when astation rotates to a position IV the sealed container is removed fromapparatus A. If for some reason, there has been a detected defect in thesealing operation, the removed container will be ejected.

In accordance with the preferred embodiment of the invention, theheating process requires 200-400 ms for the actual heating operation tobe accomplished. Since sixteen stations S1-S16 are spaced around turretT, the turret is rotated at approximately 4.0-5.0 seconds per revolutionto produce approximately 200 sealed containers per minute. Asillustrated in FIG. 1, turret T is rotated by shaft 60 about spacedbearings 62, 64 supported on the cylindrical body of a flanged sleeve 66carried on shaft 60 to rotate about axis a and with respect to a lowerfixed base 70. Sleeve 66 is clamped in position between collar 72 andupper lock nut 74. In this manner, constant velocity motor 80 rotatesturret T so that stations S1-S16 move in a circular path about axis awith a single revolution, in accordance with the preferred embodimentrequiring 4.0-5.0 seconds.

ROTARY SWITCHING

Referring now more particularly to FIG. 3, taken together with FIG. 1,rotary switch plate 100 rotates in unison with turret T and includes acontact support ring 102 into which are mounted circumferentiallyspaced, upper power contacts 104 having outwardly facing arcuate outerbrush supporting contact surfaces 106. Power contacts 104 are formedfrom a copper material to provide low electrical impedence and have acircumferential spacing which is essentially 1/16 portion of the paththrough which stations S1-S16 rotate. Each of the spaced contacts isconnected to an inwardly directed terminal 110 so that electricalcontinuity exist between each contact 104 and its associated terminal110 extending inwardly, as best shown in FIG. 3. A lower power contactring 120 has an outwardly facing, circular brush engaging surface 122and is connected to a series of circumferentially spaced terminals 124.Each station S1-S16 includes a terminal 110 and a corresponding terminal124. Of course, a single terminal 124 could be employed since ring 120is continuous; however, a plurality of terminals 124, one associatedwith each heating station on turret T, is for the purpose of preventingline differences in impedence of the bus network for directing powerthrough the rotary switch plate to the individual heating stationsS1-S16. Bolts 130 are spaced around support ring 102 for clamping rotaryswitch plate 100 into its assembled condition, as shown in FIGS. 1 and3. A fixed upper brush 140 and a fixed lower brush 142 ride,respectively, on the upper segmented copper contacts 104 and the lowerring contact 120. Consequently, electrical connection is made betweenring 120 and an individual contact 104 by the brushes 140, 142. Thesebrushes are reciprocally mounted against an appropriate compressingspring in housings 150, 152 on fixed support stand 154. This stand isbolted onto plate 160 of base 70, as best shown in FIG. 3. Power leads170 172 connect brushes 150, 152 across the output terminals of a 50KHz, high power rated power supply 180. A separate set of leads 182, 184is connected to terminals 110, 124, respectively, of each heatingstation S1-S16 so that leads 182, 184 can be individually connecteddirectly to the heating unit at these individual heating stationsS1-S16. The heating units energized by power leads 180, 184 will bedescribed in more detail later. As illustrated in FIGS. 1 and 3, it ispossible to provide rotary switch plate 100 with additional, orauxiliary, communicating systems such as a second set of contacts toprovide electrical communication between a fixed appliance or meter onapparatus A and each of the individual rotating heating stations S1-S16.To illustrate optional features, contacts 190 are circumferentiallyspaced about support plate 191 formed from insulating material. Thesecontacts coact with spring bias brush 192 and are electrically connectedwith a terminal 194 at each station S1-S16. A lower secondary contactplate 196 is fixed below plate 191 and has circumferentially spaced,narrow contacts 200 coacting with a lower spring biased brush 202 forelectrical communication with a terminal 204 associated with eachcontact 200. As turret T rotates, brushes 192, 202 electrically connectfixed leads 214, 216 with one of sixteen sets of leads 210, 212. One setof leads 210, 212 is provided for each heating station S1, S16. In thisillustrated embodiment of the invention, the secondary commutationsystem is used for a vacuum meter 220 to monitor signals through leads214, 216 indicative of the vacuum in a specific container. Brushes 192,202 direct a signal from an active set of leads 210, 212 on a givenheating station to the fixed or stationary meter 220. Of course, othermetering devices could be employed utilizing the secondary commutationsystem or second rotary switch plate concept for detecting conditions atthe individual heating stations S1, S16 as they are roated by turret T.In accordance with the invention, the basic inventive concept is in thearea of controlling energy from power supply 180 and directing thatenergy through leads 182, 184 to the individual heating station at theheating position shown as the position of station S6 in FIGS. 1 and 2.The other draw rotary switch or second commutating nework system isauxiliary to this primary concept. The commutation position need not beat any particular location around axis z, as long as it can sense thedesired parameter or condition for which it is designed.

HEATING STATIONS

Since each of the heating station S1-S2 is structurally identical, onlyheating station S6, illustrated in the heating position III, will bedescribed in detail and this description will apply equally to the otherheating stations circumferentially spaced around turret T and supportedon table 10. As illustrated in FIGS. 4, 5 and 6, the heating stationemploys a modular heating unit H which is replaceably supported onreciprocal platen 300 adapted to force the heating unit downwardly intothe sealing and heating position, as shown in FIG. 4, then reciprocatedupwardly into the retracted position. This upward disposition of unit 14allows loading of container C onto nest 30 at position I and loading oflid L onto the outer flange R of the container C at II. Platen 300carries a lower, downwardly extending connector block 302 formed ofinsulating material and connected to an upwardly extending protectivetube 304 secured onto platen 300 with block 302 by a number of bolts306, only one of which is shown. These bolts extend through the flangeon tube 304 into block 302. Protective tube 304 reciprocates in a guide308 secured to table 10 of turret T as heating unit H is reciprocatedvertically. Although not part of the invention, within the protectivetube are a plurality of conduits 310, 312 and 314 used to draw a vacuumin container C by conduit 310 and to purge the interior of the containerby passing a protective, inert gas into the container through conduit312 and out through conduit 314. This vacuum and purging function ofapparatus A assures that a minimum amount of oxygen is in the containerwhen it is sealed. Removing ambient gas from the container is standardin the food packing industry and is illussrated to acknowledge that thisfunction can be performed by novel apparatus A.

In accordance with an aspect of the invention, heating unit H is movableby hand laterally into block 302 for the purpose of connecting conduits310-314 and, more importantly, power leads 182, 184 for subsequentenergizing of the inductor or heaing ring used in practicing the presentinvention. A number of structures could be employed for rendering theelectrical connections quick-disconnect devices; however, in accordancewith the preferred embodiment of the invention, a pair of terminals 320and a second pair of terminals 322 are fixed in the insulating of block302. Terminals 320, only one of which is shown, are each connected toone of the power leads 182, 184. In a like manner, smaller terminals322, only one of which is shown, are connected individually to one ofthe auxiliary control or signal leads 210, 212. This auxiliaryelectrical connection or secondary network, which may or may not beused, includes a pair of cylindrical contacts 330, only one of which isshown. This contact has an annular groove 332 at one end of the purposeof engaging terminals 322. Female coupling members 334 coact with malecoupling members on removal of heating unit H, to be explained later,for the purpose of interconnecting two terminals of the unit or module Hwith the two terminals 322 in block 302. For the purpose of directinghigh frequency power to the unit or module H for the purposes of heatingplastic heat bondable material M to the sealing temperature, a pair ofring contacts or clamp 340, only one of which is shown, are securedaround the ends of the terminals 322. Each contact clamp 340 has anoutwardly extending alligator type, spaced coupling member 342 to coactwith a corresponding male blade or coupling member in heating unit H andshown in FIGS. 5 and 6. Movement of heating unit H laterally towardblock 302 engages the coupling members on the heating unit with the fourfemale coupling members 334, 342. Movement in the opposite directionaway from block 302 opens these four electrical connections. In thismanner, heating unit H is modular in construction and can be movedlaterally against the block 302 for the purposes of rapidly connectingor disconnecting the main power leads 182, 184 and any auxiliaryelectrical signal leads 210, 212 at each of the individual heatingstations.

Lateral movement of module or heating unit H engages the heating unitwith the lower portion of reciprocal platen 300 which can bereciprocated vertically to force the heating unit downwardly into theheating position shown in FIG. 4 and upwardly into the retractedposition to allow loading of the container and lid onto nest 30 for thepurposes of subsequent evacuation of air from he constainer and, then,sealing of the container by the heating unit H, in a manner to beexplained later. To cause controlled reciprocation of platen 300, thepreferred embodiment of the present invention includes a forcing meansor ram 360 having an upper extension carrying cam follower 362 adaptedto ride in a circular cam slot 364 concentric with axis a of turret T.Ram 360 carries a double acting cylinder 370 having a line 372 forforcing the cylinder downwardly by extending the ram and a line 374 formoving the cylinder upwardly by reracting the ram ino he closedposition. The operating element or ram of fluid operated cylinder 370 isconnected to a lower reciprocal sleeve 380 so that it can bereciprocated with respect to ram 360 by operation of the cylinder 370.To allow this movement of sleeve 380 with respect to ram 360, clearanceslots 382 are provided within sleeve 380 for both line 372 and line 374.The internal reciprocally mounted ram 380 is connected to platen 300 bya block or connector 384 adapted to be bolted onto the platen by anarrangement, not illustrated or required for the understanding of thepresent invention. Support tube 390 is fixed onto plate 10 by a flange391 and carries cylindrical sleeve bearings 392, 394. In this manner,sleeve 380 can reciprocate within support tube 390 and ram 360 can alsomove within the support tube. A female section 400 of a dovetailconnection is fixed onto the lower surface of platen 300 so that a maledovetail of heating unit H, shown in FIGS. 5 and 6, can engage femalesection 400, as heating unit or module H is moved laterally againstblock 302. An end clamp or lock plate 404 is secured by a plurality ofnuts 402 onto platen 300 for locking heating unit or module H inoperative posiion.

As the heating stations S1-S16 rotate around axis a, cam follower 302rides in cam slot 304. This slot causes the various heating units H tobe moved downwardly into an operative position with the heating unit Hadapted to move downwardly against nest 300. Thereafter, fluid isintroduced into line 372 which extends cylinder 370 and forces theheating unit downward a distance even further than the throws of camslot 364. This force can be controlled so that the desired pressure isapplied onto the lid by the heating unit H for the purpose of creatingthe pressure for holding the lid in place and forcing the lid downwardlyduring the heating operation. Consequently, cam slot 364 and camfollower 362 shift the heating unit into the operative position with thecontainer generally in an air tight area under unit H. Then the desiredpressure is applied against the heating unit to drive the rest of theheating unit downwardly to exert the desired pressure between theheating ring, to be explained later, and lid L for the purposes offorcing the lid into is sealing position with respect to the outerperipheral flange or rim R of container C. The heat bondable plasticmaterial layer M is between flange R and lid L. In practice, the lowersurface of the metallized sheet material forming lid L is coated withthe plastic bonding material M so that the bonding material is activatedonly in the area below the heating ring and between the lower surface ofthe lid and the upper surface of flange R. After the heat sealing hasoccurred, pressurized fluid in line 374 retracts the downwardlyextending he ram of cylinder 370 to move platen 300 upwardly. Inaddition, ram 360 is shifted upwardly by cam slot 364.

HEATING MODULE H

Referring now more particularly to the heating unit or module H as bestillustrated in detail in FIGS. 5-7, the individual modular heating unitscomprise a body 500 formed from an insulating material and including anoutwardly extending handle 402 for sliding the heating unit into theassembled position shown in FIG. 4 against block 302 and attached ontothe ram 360 at platen 300. At the side of body 500 facing block 302there is provided a connector 510, best shown in FIGS. 5 and 6, andincluding power coupling leads 512, 514 connected to terminals 520, 522,respectively. Power leads 524, 526 of primary winding 530 are connectedacross terminals 520, 522 to create an electrical circuit with highfrequency power supply 180, shown in FIG. 1, when the rotary switchblade connects a particular heating station S1-S16, as turret T movesthe heating station past the contacts coacting with brushes 140, 142 atthe heating position III. A square transformer core 532 has a straightleg surrounded by the primary winding and is supported on block 500 byspaced support plates 534, 536 secured onto the block by a spacing bolt538 as shown in FIG. 5. Thus, when the heating station is in the heatingposition III, high frequency power is directed through primary winding530 from coupling blades 512, 514. Signal connectors 540, 542 are alsoprovided on connector 510 for directing vacuum signals from the heatingstation to the brushes 192, 202, as previously described. This conceptis an additional feature made available by the present invention. Theseelectrical connectors 540, 542 engage coupling members 332 shown in FIG.4 and blades 512, 514 engage coupling members 342, as previouslydescribed. Thus, movement of heating unit H toward block 302 makes theelectrical connections assembled at connector 510.

In accordance with the preferred embodiment of the invention, theheating ring for heating the heat sealable or bondable material to abonding temperature is accomplished by an induction heating arrangementincluding a heating ring in the form of an inductor 560 and having ashape which dictates the footprint or pattern of a sealed seam aroundflange R of container C. Thus, the shape of inductor ring 560, whichengages the lid L and forces the lid against flange R, determines thepattern of heating the lower adhesive surface of the material forminglid L to a bonding temperature. This same ring holds the lid against theflange until the sealing has been accomplished, or stabilized to theextent that pressure can be removed by lifting ring or inductor 560 awayfrom the lid after the sealing operation. Ring 560 is especiallydesigned with the shape of container PG,25 C and its flange R. ContainerC and ring 560 are oval in the illussrated embodiment.

Ring 560, is a single turn inductor having a gap 562 defining ends ofthe inductor connected to fishtail leads 570, 572 which extend upwardlyfrom the inductor, as best shown in FIGS. 5 and 7 Brackets 580, 582 areintegrally formed with leads 570, 572, respectively, to provide a flatelectrical interface connection between the brackets and plates 584, 586which are soldered to hollow extensions 590, 592 at opposite ends of thesingle turn secondary 594 wrapped around the same leg of core 532 asprimary winding 530.

By providing this module design for unit H, the matching transformerformed by primary winding 530 and secondary winding 594 providesimpedance matching and reduces the length of the electrical circuit fromthe secondary winding to the inductor itself. Thus, there is excellentimpedance matching characteristics and low power losses. This feature isinstrumental in providing uniform operation of each unit H so that theenergy burst when measured at the power supply is an accuraterepresentation of the actual power being employed at the inductor orring 560. By providing this compact modular concept with a highfrequency transformer in the module itself, high voltage can be appliedfrom the power supply to the primary. This use of high voltage over themajor distance of electrical energy transmission reduces energy lossesby the transmissions lines from the single power supply 180 to module H.High current flow and low voltage electrical energy flows only in a veryshort, low impedance electrical circuit in the module. The secondarywinding and inductor 560 have low impedance and they are not watercooled. By being relatively large in mass and short in electricalcircuit length, ring 560 cools rapidly after it heats the metal layerprovided on the material forming lid L even without a circulatedcollant.

On connector 510 there are also illustrated a vacuum coupling 600 andpurge couplings 602, 604 which are coupled to conduits 310, 312, 314,respectively, within block 302 by normal quick-disconnect couplings ofsomewhat normal construction. Thus, the fluid lines and electricalcontacts in module H are made and established when the unit is movedinto engagement with block 302, as shown in FIG. 4. A nozzle element610, shown in FIG. 5, is used for directing the reduced pressure fromvacuum coupling 600 into the interior of the container before the lid isin place. Other arrangements could be employed for both vacuumevacuation of the container and gas purging of the container which isaccomplished by apparatus A as the individual heating stations S1-S16are moved in the circular path by turret T.

To support inductor 560 onto body 500, there is provided an internalsupport plate 620, which may include flux concentrators, and an outerinductor holder 622 which can also include flux concentrators. Thesupport plate of holder sandwiches the inductor to rigidify it for thepurpose of allowing the inductor to create pressure against the lid asthe lid is forced into place by the lower portion of holder 622. Thus,the holder 622 and inductor 560 engage the upper surface of lid L forforcing the lid downwardly. Thereafter, high frequency power is suppliedto heating unit H from power supply 180 by way of the rotary switchplate to cause a current flow in the inductor of unit H. This induceshigh frequency current flow adjacent inductor 560 in the metal layer ofthe laminated lid for the purposes of heating that metallized layerbelow ring or inductor 560. This in turn heats the adhesive or plastic,heat bondable material on the lower surface of the lid for sealing theportion under the inductor onto the flange R of container C. An outerO-ring seal 624 seals holder 622 with respect to a reciprocal hold downring 630 having a downwardly extending O ring seal 632 for engaging theupper surface of nest 30, as shown in FIG. 4, for providing a sealaround the nest so that the area above the container can be evacuatedand gas purged as previously described. Thereafter, lid L is forced intoplace by the lower surface of inductor holder 622 and the inductoritself for the purposes of forcing the lid into the sealing positionpreparatory to heat sealing by on induction heating process.

To support heating unit H on platen 300, there is provided a male doveelement 640 on an integral plate 642 bolted to the upper surface of body500 by a plurality of transversely spaced bolts 644 best shown in FIG.4. As modular heating unit H is moved transversely into the operativeposition, dovetail element 640 engages element 400 for coupling thereplaceable modular, heating unit H with block 302. The electricalconnections are made and unit H is captured by platen 300 forreciprocalaction as described above.

HIGH FREQUENCY HEATING AND ENERGY CONTROL

Power supply 180 is fixed relatively to rotating heating stationsS1-S16. The high frequency is a radio frequency greater than 25 KHz andpreferably greater than 50 KHz. In practice, the power supply is a 50KHz solid state inverter having a high voltage output for transmissionalong relatively long bus lines between the power supply and theindividual contacts of the rotary switch plate. In this manner, there isa relatively low current flow and loss through the input bus network.Since the output bus network is essentially the electrical components inthe heating unit or module H, there is relatively high efficiency fromthe power supply to the individual inductors 560 at the various heatingstations. In accordance with the present invention as described in theintroductory portion of this disclosure, the actual energy supplied toeach heating station for processing and sealing each lid onto a givencontainer is monitored by a power monitor network schematicallyillustrated in FIG. 8. An appropriate volt meter 700 measures theinstantaneous voltage from the power supply and an approriate currenttransformer 702 measures the instantaneous current flow as indicated bycurrent meter 704. In accordance with standard practice, these twoinstantaneous signals, one representing instantaneous voltage and onerepresenting instantaneous current from the power supply itself aremeasured at the power supply and are combined by a watt meter 710 tocreate an instantaneous watt voltage signal output in line W. Inaccordance with a modification of this general concept, it is possibleto create a constant trace or sampled trace for both the voltage andcurrent as indicated by blocks 512, 514. These traces can be compared bya microprocessor with a fixed trace stored in memory in accordance withstandard power monitoring techniques to determine whether or not theinstantaneous voltage or current profile for a particular heating cycledeviates beyond preselected limits from a fixed trace or profile. Ofcourse, other arrangements could be provided for obtaining theinstantaneous power supplied during a heating cycle performed at anindividual heating station being driven or energized by power supply180. The arrangement illustrated in FIG. 8 is schematic in nature and isused only to illustrate that the current and voltage is combined toproduce an instantaneous power signal. Of course, the power signal couldbe introduced into a trace, recording or reading device, including apreselected profile, for the purposes of determining variations in thepower as well as variations in the current and voltage. In someinstances, the power supply can be monitored to produce variations inthe power factor between the current and voltage which power factorvariation is introduced into a trace device or network having a fixedprofile or map so that the differential in measured power factor can beemployed to determine such things as misplaced lids and other defectswhich will cause a rejection of a particular lid being processed. Thus,if the lid is misplaced or a sealing operation is improperlyaccomplished, this defect can be identified by one of the trace devicesas measured by current, voltage, power and/or phase shift. The schematicdiagram shown in FIG. 8 is the input for accomplishing these objectivesand creates a power signal represented by line W between the powersupply portion of the circuit and heating unit H. The interruptedportions x, y are indicative of the communicating connection between thefixed power supply and control system at the left and the rotary at theright. Of course, the quick disconnect arrangements are not illustrated.An inductor 720 is illustrated as being in the secondary bus network ofthe power supply itself to improve the efficiency of energy transferredby smoothing variable conditions.

Referring now to FIG. 9, details of the control of power supply 180 todictate energy profiling during the treating cycle is illustrated. As abackground control, power supply 180 is initiated, i.e. turned on, attime T1 and is stopped, i.e. turned off, at time T2 which is amicroprocessed or created signal to override the energy control systemand establisxh a maximum cycle time as will be explained later.Referring to the logic diagram of FIG. 9, which is used to explain theenergy control system starting element, illustrated as flip flop 800 isreset upon an output signal 862a from AND gate 802. The CONTACT terminalof this gate indicates that there has been an electrical connectionbetween the brushes and the moving contact at a heating station to whichan energy brush is to be directed for heating the bondable material. Inother words, when there is electrical contact a CONTACT signal iscreated. At the starting time, thereafter, a T1 signal is created by themicroprocessor and an output appears in line 802a. This turns the radiofrequency power supply 180 on. Power is then supplied to inductor 560 ofthe particular heating unit in the heating position until the powersupply 180 is deactivated. The concept represented by flip flop 800provides an override deactivation circuit for turning the power supplyoff before the dry switch is disconnected. A CONTACT or time T2 signalfrom the microprocessor appearing at the input of OR gate 804 to setflip flop 800 when the time expires (T2) or contrast is to be broken.The CONTACT terminal is at a logic 1 as the electrical contact betweenthe rotary switch plate and the rotating heating station are neardisengagement. CONTACT indicates when there is to be disengagement ofthe sliding contact and brushes. When that condition is approaching, alogic 1 appears at gate 804, which sets flip flop 800 to produce a logic1 in output line 800a to energize a signal light 800b or other typeflag. This condition is not, in the preferred embodiment, a preferredmode of operation. Power supply 180 should be deenergized beforeapproach CONTACT position. The CONTACT signal is an override to assurethat the power from the power supply is turned off before there is abreak in the electrical connections which could cause harmful arcing.Another way to prevent this harmful arcing is the provision of theterminating time signal T2 created by the microprocessor. This signalforms the other input of gate 804. Consequently, at the end of a timeperiod (T1-T2) or when there is a sensed positionally condition that thecontacts are ready to separate, flip flop 800, or another appropriateprogramming device, is energized to deactivate the power supply. This isindicated as a reject condition by a programming scheme schematicallyillustrated as a reject light 800b. In the preferred embodiment of theinvention the length of the heating cycle is not controlled by eitherthe physical position of the heating unit or a fixed time indicative ofthe T2 condition. However, in accordance with the broadest aspect of theinvention, both of these inputs, i.e. T2 or the approach of CONTACTcould be employed for deactivating the power supply. This method andsystem could be incorporated with the turret concept to producesatisfactorily sealed containers; however, the present invention istechnically advanced over that rudimentary control of the basic conceptof the present invention.

In accordance with a novel operating procedure used in accordance withanother aspect of the invention, power supply 180 is controlled by anenergy monitor schematically represented as block 820 having an input822 indicative of instantaneous wattage from output line W of watt meter710 in FIG. 8 and a clocking or time input 824, which is indicative ofreal time t. The output of energy monitor 820 is the accumulated energyof a single burst used in a single heating cycle, as measured by thesummation of the product of input terminals 822, 824. This accumulatedenergy appears as a voltage level or an incremented digital signal inline 826. Energy monitor 820 is reset at time T2 from themicroprocessor, as indicated by reset line 828. Thus, a microprocessorcreated signal at input 822 resets the energy monitor to accumulate theenergy for the next successive heating cycle of power supply 180, whichis initiated by a signal in line 802a to enable the energy monitor asindicated by ENABLE line 830. Thus, energy monitor 820 is started andaccumulates the actual energy being directed from power supply 180 toinductor 560 when a signal appears in line 830. The energy monitor isreset and waits for the next heating cycle by a microprocess or createdtime T2 signal in line 828. The accumulated energy in a given heatingcycle appears in output 826 which is directed to a compare network 840for comparing the accumulated energy from energy monitor 820 with apreselected energy limit from an energy limit stored in themicroprocessor memory, illustrated conceptually as block 842. Thepreselected and/or microprocessor created magnitude of output energy isdirected by line 844 to comparator 840 so that the digital or voltagesignal in line 826 is compared to the same type signal in line 844 bycomparator 840. When a comparison has been acknowledged, indicating thatthe desired amount of energy has been used in a given heating cycle, anoutput signal appears in line 846 and is directed to OR gate 850 having,as its second input, the output logic of flip flop 800 on line 800a.Thus, when the desired amount of energy has been supplied for a heatingcycle, a signal or logic on line 846 creates a logic 1 in output 852 ofgate 850 to turn off or deactivate power supply 180. This power supplycan be turned off by the override signal in line 800a caused by either atime out at T2 or an approaching contact break, either of which willcause an output signal from OR gate 804.

In the simplest form of the energy monitor and comparator networkcontemplated by the present invention, the stored amount of energy inenergy limit device 842 is a fixed magnitude. Thus, when the fixedamount of energy is developed by the power supply during a given heatingcycle, the power supply is deenergized. In accordance with still furtherimprovements in this basic concept, there is provided an arrangementincluding a further storage location in the microprocessor memory foridentifying which of the various stations (S1-S16) is being processed.Thus, the energy limit can be loaded from memory for a particular energyburst for a particular heating station as represented by block 860. Inthis manner, each heating station can have its own preselected premappedstored energy for the heating cycle. In addition, the energy limits canbe modified on a real time basis by using an I/O network to produce testpoints as indicated by lines 862, 864. Parameters, such as trendanalysis or actual physical conditions existing at each of the variousheating stations, can be inputted to modify the actual energy level foreach of the various positions. Consequently, by using the presentinvention, if it is found that the energy levels for one particularstation has a trend, the trend can be detected as a real world conditionby sensing test points and the energy level can be modified ormonitored. To perform this function, there is illustrated a recordernetwork 870 which can be enabled by the starting signal T1 created bythe microprocessor and can be disabled by the OFF signal in line 874.The microprocessor identifies the particular heating station beingmonitored and recorder network 870 records the energy employed for thatparticular heating cycle. In addition, the energy burst can beintegrated with respect to time to produce a recorded trace of theenergy similar to the current, voltage and power trace set forth in FIG.8. Recorder network can be employed for data tp adjust the set points ofthe energy limit 842 and can also be employed for the purpose of qualitycontrol and trend analysis. Referring now to FIG. 9A, the instantaneouspower and time can be integrated between T1 and T2 by an integrationcircuit 900 and summed, if necessary, in accumulator 904 to produce aunique power/time integration for incrementally summarizing the totalenergy delivered to the inductor by incrementally multiplying the truekilowatts by time. This particular integration is advantageous for highspeed reading rates to handle the short heating cycle length involved inthis particular embodiment of the invention, which cycle lengths arebetween 100-400 ms. These heating cycles are schematically illustratedin FIG. 10 as being approximately 300 ms and occurring sixteen timesduring a single revolution of the turret T. Thus, the heating cycle HCand the waiting period between the heating cycles is approximately100-400 ms. Each of these heating cycles is a particular cycle,controlled by the circuit schematically illustrated in FIG. 9. Ofcourse, this circuit is normally digitally controlled by amicroprocessor and the blocks and gates are used to illustrate theoperating characteristics of the program employed in cycle themicroprocessor. The showing is not indicative of actual hardwarecircuitry employed in practicing the invention.

Referring now specifically to FIG. 11, heating cycles HC start when theinductor is moved down into the sealing position. Thereafter, electricalcontact is made between the rotary switch plate and the fixed brushesfor a particular one of the heating stations S1-S16. Thereafter, themicroprocessor produces the time signal T1. If the electrical contacthas been accomplished, a CONTACT signal is produced. j When both CONTACTand T1 exist, a signal on line 802 of FIG. 9 energizes power supply 180.In accordance with another aspect of the invention, the power supply isramped up in less than 20 ms and preferably in the range of 10-20 ms, asindicated on FIG. 12, to the normal operating power level indicated bythe upper generally straight line of each heating cycle HC. At time T2,which is before the electrical connection has been broken, power supply180 is deenergized. In the preferred embodiment of the invention, thisis a fault condition since the energy monitor 820 should deenergizeheating cycle HC, as represented by the dashed lines, before a time T2.Thereafter, inductor or heating ring continues to press against the lidfor seal stabilization to assure that the adhesive action of the heatbondable material has been set or fixed. Then the inductor is moved upand the next heating cycle HC is initiated.

FIG. 12 illustrates a further modification of the present inventionwherein the power level from the power supply 180 has two separateoutput levels a, b. In time T1, power is supplied at a maximum level a.At time T3, well before time T2, the power supply is shifted from thisupper level a to lower level b and remains at this level until theaccumulated energy limit has been reached or a T2 signal is created,which ever occurs first. This produces a relatively rapid heating of thebonding material to the heat temperature, then maintains thistemperature for a preselected time preparatory to entering the sealstabilization area of the total operating cycle as illustrated in FIG.11. This modification of the present invention is contemplated and doeshave some advantages which can be realized only with induction heating.The preferred embodiment of the invention uses the energy burst or cycleset forth in FIG. 11.

Having thus defined the invention, the following is claimed:
 1. Amodular type replaceable heating unit for use in a device for sealing aflat lid with a lower layer of heat bondable material onto an upper,generally flat flange extending around the periphery of an accessopening in a container, said sealing device including a plurality ofsaid heating units, means for sequentially moving said modular heatingunits vertically to and away from said lid, a power supply, a connectorfor each heating unit electrically connected to said power supply havinga first pair of electrical contacts which are stationary relative tosaid moving means, said modular heating unit comprising: (i) a housingadapted to be mounted to said moving means; (ii) an inductor extendingfrom the lower portion of said housing and adapted to seat against saidlid for heat sealing said lid to said flanges; (iii) a matchingtransformer within said housing, said transformer having a secondaryconnected to said inductor and a primary; (iv) a pair of bayonet typesecond contacts extending from said housing and electrically connectedto said primary; and (v) cam means extending from said housing forselectively connecting said second contacts with said first contactsupon movement of said housing whereby said transformer and said inductoris energized by said power supply.
 2. A heating unit as defined in claim1 wherein said sealing system includes stationary passage means fordrawing a vacuum, and said heating unit includes passage means adaptedto be in fluid communication with said container, said cam meansoperable to connect said stationary passages with said passage meansupon movement of said housing whereby a vacuum can be selectively drawnin said container.
 3. The heating unit of claim 1 wherein said secondaryis a single turn winding, and said inductor is a single turn air cooledonly inductor.